The present invention relates to a system for amplifying and shaping optical pulses without converting them into electric signals. Such a system is useful as, for example, an optical repeated optical communication system.
One of technical fields requiring the amplification and shaping of optical pulses is optical communication. In optical communication, especially in an optical communication system employing optical fibers as transmission media, a long transmission distance subjects optical signals to great attenuations and waveform distortion. In order to cope with this drawback, it is common practice that optical repeaters are disposed at suitable intervals so as to compensate for the attenuations and waveform distortions of optical signals. The optical repeaters include two types. The first type converts an optical signal into an electric signal, then processes the electric signal, and converts the processed signal back into an optical signal (refer to `Hikari Tsushin` [Optical Communication] edited by Seiji Ohara and Tatsuya Kimura, published by Corona Pubishing Co., Ltd. in 1981, pp. 222-223). This first type of repeater comprises an optical detector which converts an arriving optical signal into an electric signal, a regenerating repeater which amplifies and shapes the obtained electric signal, an optical source which converts the electric signal into an optical signal, and a drive circuit which drives the optical source. The regenerating repeater consists of an equalizing amplifier, a timing extraction circuit and a decision circuit. By employing the first type of repeater, the compensation of attenuation and the removal of waveform distortion can be performed, but a large-scale and complicated circuit is necessary.
Second type of optical repeater employs an optical amplifier and directly amplifies an optical signal without converting it into an electric signal (refer to `Hikari Tsushin` mentioned above, p. 264). When using a semiconductor laser as the optical amplifier, a laser driving current is maintained at a value just below a threshold level, whereupon when an input optical signal is injected into an active layer, optical amplification of the laser occurs to transmit an amplified optical signal. by employing this second type of repeater, a small-scale and simple circuit suffices, but existing waveform distortions cannot be removed because the input optical signal is amplified as it is and then transmitted.